Alright hive mind, tell me what this is. The one time I swung out to the dealership to have them take a listen, it wasn't happening. Figured I'd slap an SD card in and see if PDR can capture it, and sure enough, on the first drive out it was particularly loud.


0:19 you can hear it go away as the revs fall, but it comes back once at idle. Engine is at full operating temperature fresh off the freeway.

It doesn't appear to be temperature related.
It's intermittent, but seems to happen 80+% of the time.
It either isn't happening or is drowned out by engine noise once moving.
Coasting in neutral at 20mph or higher I cannot hear it -- could be drowned out by road noise.
Most audible inside the car.
Difficult to hear from above the car.
Impossible to hear over the injector clatter from under the car (if it was even happening while I was under it).


Right now I'm torn between an exhaust leak at the head and direct injection noise -- though, if it's the DI, that's easily the loudest DI system I've heard, diesels included.

 

Well, the lack of seventeen people immediately coming in and saying "yep that horrible noise is totally normal god bless america" is indication enough that something ain't right.

Thanks gents!

 

Does it matter if the clutch is in our out? Asking because you went right to neutral versus holding the clutch in. Yeah, that's a pretty pronounced noise for sure.

Two things I'd work to rule out, first is belt tensioner and second torque tube. Both are RPM sensitive.

 

Clutch doesn't have any impact. Dragging it against the brakes at a standstill to put some tension in the drivetrain doesn't change anything. I'm reasonably sure it isn't the torque tube, but only because I didn't hear it very loudly while standing under the car. Another member here had a similar sound, at least by description, that turned out to be an exhaust leak at the head.

Belt tensioner is an interesting one. Perhaps the belt flapping around at low RPMs? I do recall reading that they were failure prone.

Went on a short drive tonight after taking apart the airbox to check the air filter. Potentially new behaviour -- the rattling sound will very suddenly and abruptly go away sometimes, now. Usually it would fade in and out, not start/stop abruptly.

 

Thank you for the additional info, I'm really interested to see what you find out. Sporadic noises can be so hard to pinpoint.

 

It doesn't seem to change with RPM -- listen between 0:15 and 0:25 in the video where it's revved up. To my ears that sounds about the same as when idle, which is under half the RPM of what I revved to.

In my mind that rules out ignition or injection events, which rules out exhaust leak. It also rules out rotational items, such as the belt drive.

 

Just jiggled the hood to rattle it against the latches. GF and I both agree that while it sounds similar, that's not the same sound -- it'd also be crazy loud outside the car if it were.

I'll have to put it up in the air and take a good look around the firewall. Might just be some kind of tube or loom not strapped down, rattling against the firewall.

 

So interesting it's almost inaudible when you let off the throttle yet returns when it settles. And it is audible during the entire time you raise rpms. Does it get even faster if you increase rpm's past what you did in your video?

So strange.

 

Above around 2k the overall noise of the car is either drowning out the sound, or the sound stops happening. For the entire time I can hear it though, the rate seems to be constant, which is really throwing me off.

 

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Well the good(?) news is that it's seeming to be getting worse, so the dealership will probably be able to diagnose it soon!

It's still doing the weird abrupt start/stop behaviour.

Starting to notice what I would describe as excessive driveline slack, not sure if it's related. The car can't idle in first or second gear at this point (or ever? Can't remember), it will start bucking violently if you try.

 

I hope you get this sorted out. I have not heard of anything like this.

 

I'm no mechanic, but maybe it's the fuel pump since it isn't mechanically related to engine or drive speed?

 

The sound is coming from the engine bay, not the hatch area. :\

 

Any update on this?

 

Nope, the dealership ghosted me. Gotta reach out again.

 

This makes me mad and it isn't my car

 

Same. Haven't chased this down much, we got some really terrible weather patterns that make driving the corvette an exercise in anxiety, what with the icebergs jutting up from the streets. Car's riding lower than factory spec, not sure if things settled or the p/o found a wrench.

 

AC blower fan?

 

Finally got something scheduled, gonna be dropping it off tonight.

My findings in the meantime...

The sound is happening at 17hz. The engine spins at 10 to 10.8hz at idle (600-650rpm), and it also continues to be audible when the engine is spinning at 22.5hz (1350 rpm). When at 1350rpm, the sound is still happening at a rate of 17hz, which means it is not tied to RPM. We can reasonably assume it's not injection, ignition, belt drive, or valvetrain related.

It happens with or without the clutch pushed in, which reasonably eliminates the torque tube internals.

It stops happening as revs are falling, but picks back up when ignition events start happening again.

My only thought at this point is it is an engine mount or something related to the physical motion of the engine.

The car is CPO and this is an issue that only happens when the engine is on, so my argument is that it is drivetrain related. Hopefully they don't try to gouge me with diagnostic fees and the like -- I've cleared dropping it off for evaluation and no pricing or charge approval was discussed, so things are looking good on that front.

More to come.